1. Field of the Invention
The present invention relates to a method of manufacturing a pipe liner bag for use in repair of an old pipe.
2. Description of the Related Art
When an underground pipe, such as pipelines and passageways, becomes defective or too old to perform properly, the pipe is repaired and rehabilitated without digging the earth to expose the pipe and disassembling the sections of the pipe. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. The pipe lining method utilizes a tubular pipe liner bag made of a resin absorbent material impregnated with a hardenable resin, and having the outer surface covered with a highly air-tight plastic film. The tubular pipe liner bag is inserted into a pipe to be repaired by means of a pressurized fluid such that the pipe liner bag is turned inside out as it proceeds deeper in the pipe. Hereinafter, this manner of insertion shall be called "everting". When the entire length of the tubular liner bag is everted (i.e., turned inside out) into the pipe, the everted tubular liner is pressed against the inner wall of the pipe by a pressurized fluid, and the tubular flexible liner is hardened as the hardenable resin impregnated in the liner is heated, which is effected by heating the fluid filling the tubular liner bag. It is thus possible to line the inner wall of the defective or old pipe with a rigid liner without digging the ground and disassembling the pipe sections.
The pipe lining material for use in the foregoing pipe lining method may be manufactured by a method proposed, for example, in Japanese Patent Publication No. 58-33098. Specifically, this method involves abutting both side ends of a strip-shaped resin absorbent material in the width direction, and joining, by lock sewing or zigzag chain sewing, the abutted ends of the strip-shaped resin absorbent material to form a tubular resin absorbent material.
However, the lock sewing or zigzag chain sewing, employed in the conventional manufacturing method, is late in sewing, as compared with straight sewing such as final sewing or through sewing. In addition, since a sewing yarn appears on the surface of a sewed material over a constant width, the sealability cannot be ensured for the joint unless any processing is added thereto. Such sealing processing causes an increased complexity of the manufacturing method.
A pipe liner bag is inflated within a pipe line by the action of a fluid pressure and pressed onto the inner wall of the pipe line. To prevent the pipe liner bag from wrinkling, the pipe liner bag is typically manufactured to have a smaller diameter than that of an intended pipe line. Thus, if the pipe liner bag extended by a fluid pressure is applied with a tension, the sewed portion is extended and reduced in thickness, resulting in an insufficient strength. It is therefore necessary to reinforce the sewed portion of the tubular pipe liner bag by additionally adhering a reinforcing tape or the like thereon.
There has been proposed a method of manufacturing a tubular resin absorbent material by overlapping both end portions in the width direction of a strip-shaped resin absorbent material, and sewing the overlapped end portions by straight sewing such as main sewing, through sewing or the like in order to reduce a time required for a sewing process as well as to narrow a width of the strip-shaped resin absorbent material required for the sewing to simplify a sealing operation for a joint.
With this method, however, a sewing margin remains at the joint on the outer surface of the resultant tubular resin absorbent material, and may cause an impediment in covering a plastic film over the outer surface of the tubular resin absorbent material. Thus, a sealing process or an air-tight sealing process is difficult to perform on the tubular resin absorbent material with a plastic film unless any processing is added to the sewing margin.